ObjectInputStream returning EOFException when reading List of Object

Question

Im returning a list of all the objects stored in some temporary files in my Android project. When the list its appended the file its deleted.

    public static <T> List<T> fileToLogList(Context context) {
        String path = context.getFilesDir()
                .getAbsolutePath();
        List<T> list = new ArrayList<>();
        FileInputStream fis;
        try {
            File directory = new File(path);
            File[] files = directory.listFiles();
            for (File file : files) {
                fis = new FileInputStream(file);
                ObjectInputStream ois = new ObjectInputStream(fis);
                list.addAll((List<T>) ois.readObject());
                ois.close();
                fis.close();
                context.deleteFile(file.getName());
            }
        } catch (FileNotFoundException e) {
            return new ArrayList<>();
        } catch (IOException e) {
            throw new RuntimeException(e);
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        }
        return list;
    }

The problem is that sometimes ois.readObject() will return a EOFException. I dont understand the accepted answer of the following question. I have tried the second answer and it also returns an exception.

E/AndroidRuntime: FATAL EXCEPTION: Timer-1
    Process: com.example.application, PID: 774
    java.lang.RuntimeException: java.io.EOFException
        at com.example.application.utils.Utils.fileToLogList(Utils.java:172)
        at com.example.application.logging.LogService$2.run(LogService.java:31)
        at java.util.TimerThread.mainLoop(Timer.java:562)
        at java.util.TimerThread.run(Timer.java:512)
     Caused by: java.io.EOFException
        at java.io.ObjectInputStream$BlockDataInputStream.peekByte(ObjectInputStream.java:2751)
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1378)
        at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2114)
        at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2038)
        at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1899)
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1412)
        at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2114)
        at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2038)
        at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1899)
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1412)
        at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2114)
        at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2038)
        at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1899)
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1412)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:427)
        at java.util.concurrent.CopyOnWriteArrayList.readObject(CopyOnWriteArrayList.java:931)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1066)
        at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2013)
        at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1899)
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1412)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:427)
        at com.example.application.utils.Utils.fileToLogList(Utils.java:164)
        at com.example.application.logging.LogService$2.run(LogService.java:31) 
        at java.util.TimerThread.mainLoop(Timer.java:562) 
        at java.util.TimerThread.run(Timer.java:512)

Lastly this is my method to write into the files:

    public static <T> void logListIntoFile(List<T> output, Context context) {
        FileOutputStream fos;
        try {
            // writes into a file named YYYY-MM-DD_HH:MM
            fos = context.openFileOutput(getCurrentDateMinutes() + ".tmp", Context.MODE_PRIVATE);
            ObjectOutputStream os = new ObjectOutputStream(fos);
            os.writeObject(output);
            os.close();
            fos.close();
        } catch (FileNotFoundException e) {
            throw new RuntimeException(e);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

Michał Marcinkowski · Accepted Answer · 2023-02-27T15:04:27.223

Basically - EOF exception might be thrown in two situations,

when you've reached end of file and there is nothing more to read
when the file is corrupted

If you're leverage reading from file on EOF exception then you won't be able determine which one is the actual source of the problem. Do you need to to detect this difference? If not - base reading on EOF exception

What the author of mentioned answer suggested (at least I understand it this way), to use some RandomAccessFile approach, in which apart from the actual list of objects you would store an integer as first object which will tell you how many files are there.

Have you considered if aren't there a situation in which those reads and writes are called simultaneously? If you're trying to read a file in between some different is writing to it, such a situation may happen.

Personally I'd try to add some synchronization, to postpone writing until reading is finished and then see what is gonna happen because I believe this is the root cause of the problem.

"to postpone writing until reading is finished and then see what is gonna happen." I have tried to look into ways to make the file writing thread safe but I havent had any luck whatsoever, do you perhaps have any code examples that might point me to the right direction? — Daniel Hernández, Feb 27 '23 at 14:58
I do not have one, but it is rather simple. You may use AtomicBoolean isReading = new AtomicBoolean() and share it between those two methods. At the beginning of the reading method you set it to true, at the end to false. Then wrap all the code in the writing method with while(isReading), at the end of that while(isReading) block, add some System.sleep(500) to delay another attempt of writing. — Michał Marcinkowski, Feb 27 '23 at 15:03

ObjectInputStream returning EOFException when reading List of Object

1 Answers1